Yes and no
Software copyright should officially expire after 20 years...
That should read "Proprietary software copyright should officially expire..." and maybe you need to add "abandoned/orphaned" too.
You'd probably create a huge problem too. The point of copyleft FOSS is that it remains available. That is the crux of many FOSS licences, where it uses the copyright legislation to retain user's rights.
A lot of FOSS projects are older than 20 years. Do you want them to become more open than open by removing the copyright protections? How do you deal with many FOSS projects' continual development cycle where part of the code is ancient and some is brand new. How do you distinguish new and old code? Line 1 gets no protection and line 2 gets protected? After a bugfix, characters 5..17 of line 413 are protected while the rest of the file is not?
If you want to expire copyright after a short time, then you need to make a new class of global legislation to put copyleft on the books.